Genetic and biochemical studies have identified two major points of control for progression through the eukaryotic cell cycle. These decision points are the transition stages between the G1 phase and DNA synthesis (G1/S) and between the G2 phase and mitosis (G2/M). Over the last few years, several points that regulate progression through these restriction points have been identified. Much of this work has centered on the product of a cell division control gene, cdc2. The cdc2 gene encodes a protein of 34,000 daltons (p34) that is essential for progression through both the G1/S and G2/M restriction points in budding and fission yeast. Progression through G2/M is controlled by a multimeric protein complex having an intrinsic kinase activity that is maximally active in mitosis. p34 is the catalytic subunit of this kinase, and this complex is now known about how progression through the G1/S transition is regulated. Recently, a second protein complex that contains the p34 protein has been discovered. In human cells, p34 also associates with a 60,000 dalton protein known as p60, and this complex has a cell cycle-regulated kinase activity as well. However, unlike the mitotic p34-containing kinase, the p60/p34 complex is activated beginning at the G1/S boundary. Thus, the p60/p34 complex is a candidate for a regulator of the G1/S transition. What makes the identification of this second p34 complex particularly interesting is that p60 has been identified previously. It was originally identified through its association with the E1A proteins of adenovirus, proteins that are known to modify cell cycle regulation. Work in this grant will investigate the role of the p60/p34 complex in cell cycle regulation. The p60 protein and the p60/p34 complex will be characterized and compared to the better studied mitotic p34 complex. The activation of the p60/p34 kinase will be compared to the better studied p60 and p34 synthesis, phosphorylation, and association. Also we would like to know how a viral protein such as E1A, which is known to act as a mitogen, affects the function of the p60/p34 complex and whether these changes help explain E1A's ability to act as a oncogene. In addition, if other proteins that resemble p60 can be identified, they will be characterized. A great deal of research over the last several years has attempted to link the biochemical activities of various oncogenes directly to changes in cell cycle control, and the discovery of the physical association between that of a potent oncogene and a potential regulator of cell cycle control promises to provide a unique opportunity to investigate these connections.